This invention relates to the field of interconnect structures for interconnecting electronic modules, and more particularly, this invention relates to an interconnect structure for interconnecting electronic modules that reduces the required number of coaxial cables used to interconnect the electronic modules.
Typical avionics applications used in high performance aircraft and similar end uses employ electronics modules that are blind-mated into racks. These modules require a large number of RF input/output connections for digital, analog and optical signals. Non-limiting examples include coaxial connectors for radio frequency connections, pigtail, splice or small form function optical connectors, and digital connectors, all known to those skilled in the art. As shown in FIG. 1, a module interface 20, such as part of a printed circuit board backplane, interfaces with various signals and power supplies using different connectors. These signals include analog, including RF signals, optical, low and high power RF, and power. Some module-to-module interconnects must operate at RF frequencies as high as 30 GHz. In some applications, the RF signals above 1 GHz are routed between modules within the same rack using coaxial cables, which has provided the necessary combination of high reliability, low loss, and controlled impedance at these frequencies. The coaxial cables are terminated with spring-loaded connectors that protrude through holes in a digital motherboard forming a backplane and then are attached to respective connectors. Behind the motherboard, the cables are routed in circuitous paths and supported to the motherboard by a variety of different securement mechanisms.
When many RF interconnects are used, the coaxial cables consume a large volume behind the motherboard, and as a result, their routing becomes complex and difficult. To fabricate a module assembly in this manner is difficult if a large number of coaxial cables are required. The available space may not permit proper routing between adjacent modules, and as a result, the cable connectors cannot be assembled onto the motherboard. Even if the cables are secured, they may not adequately float to allow proper mating to the module. Furthermore, the desired number of RF input/output (I/O) connectors on a single module may be large, such that the resulting spacing between I/O connectors cannot be accommodated with cable connectors.
Another drawback of these prior art backplane assemblies is their propensity to deflect under static loads caused by module insertion, and dynamic loads caused by vibration. Static deflections increase the chance of incomplete connector engagement, preventing proper operation. Static and dynamic deflections cause failure of the circuit traces within the printed circuit board, or failure of electrical components mounted on the surfaces. Dynamic deflections of a backplane wear a connector""s internal contacts, eventually leading to failure of the connector. Dynamic deflections also cause phase noise induction on sensitive RF signals.
The present invention is advantageous and eliminates the large number of coaxial cables required for interconnecting various electronic modules. It incorporates a low-loss backplane assembly having a substantially rigid backplane plate that allows both digital and analog signals to be transmitted using various RF and digital connectors. It is also possible to use spaced optical connectors.
In accordance with one aspect of the present invention, the interconnect structure includes a backplane assembly that interconnects a plurality of electronic modules. This backplane assembly includes a substantially rigid backplane plate having a rear surface and a front surface that interfaces with electronic modules. A plurality of radio frequency (RF) connectors are carried by the backplane plate and extend from the front to the rear surface for receiving mating RF connectors of electronic modules.
A digital motherboard is formed as a printed circuit board and supported by the backplane plate. It includes digital connectors, as known to those skilled in the art, for mating with digital connectors of electronic modules. A controlled impedance interconnect circuit is positioned on the rear surface of the backplane plate and interconnects the RF connectors carried by the backplane plate and digital connectors of the digital motherboard. A rack receives the backplane assembly and supports a plurality of electronic modules that are interconnected to each other via the backplane assembly.
The controlled impedance interconnect circuit can include a plurality of waffleline grooves formed within the rear surface of the backplane plate. Waffleline wire can be received within the waffleline grooves and interconnect the RF connectors. These connectors can be formed as coaxial connectors having coaxial connector pins that extend to the rear surface on the backplane plate and are interconnected to each other by the controlled impedance interconnect circuit. The backplane plate can include formed cavities having holes that are dimensioned to receive the coaxial connectors.
In yet another aspect of the present invention, the controlled impedance interconnect surface can be formed from channel line or as a stripline circuit card carried by the rear surface of the backplane plate.
In still another aspect of the present invention, the rack and backplane plate are formed from a metallic material and are substantially similar as to their coefficient of expansion (CTE). A motherboard cavity receives the digital motherboard formed as printed circuit board and has openings extending to the front face through which the digital connectors extend for interfacing with digital connectors of electronic modules. Guide holes receive counterpart guide pins on an electronics module for aligning the electronics module with the backplane plate. The rack can include guide channels that receive guide members of an electronics module for aligning an electronics module with the backplane plate. The electronics module can act as a heat sink where the guide members of the electronics module in conjunction with the guide channel are operative for transfer of heat.
In yet another aspect of the present invention, a rear cover is formed of a metallic material that is substantially similar as to its coefficient of expansion with the backplane plate and supports the backplane plate thereto. The rear cover is secured to the rack and covers a portion of the rack and protects the rear surface of the backplane plate and any controlled impedance interconnect circuit positioned on the rear surface of the backplane plate. The rear cover can include formed cavities that cover any waffleline grooves with wires for connection to RF connectors. The cavities have peripheral walls that aid in isolating electrical signals routed through the waffleline grooves from other portions of the backplane plate.